The present invention relates to image forming apparatuses provided with a waste toner full-capacity detection mechanism.
In electrophotography image forming apparatuses, toner adhering to the surface of a photoreceptor is transferred onto a sheet, and the toner on the sheet is fixed to complete image forming process. The toner adhering to the surface of the photoreceptor is transferred to the sheet by electrical action. A part of the toner, however, remains on the photoreceptor surface, and therefore a mechanism to collect such remaining toner is needed. To this end, electrophotography image forming apparatuses are provided with a waste toner box to collect the not-transferred toner remaining on the photoreceptor surface after the image forming process and store a predetermined amount of such waste toner therein.
These image forming apparatuses are provided with a detection sensor to detect the amount of toner stored in the waste toner box. This detection sensor can detect, on the basis of the weight of the waste toner box placed on a waste toner box base, the end state where the waste toner box is full of waste toner as well as the near-end state where the waste toner box is almost full of waste toner. The near-end state is for informing a user of such a state and letting the user replace the waste toner box before the waste toner box becomes full of the waste toner because the image forming apparatus in the end state no longer can execute the image forming process.
The near-end state, however, is canceled in some cases by shaking or tapping the waste toner box in the near-end state, and repeated cancellation of the near-end state to continue the image forming process may cause waste toner to be collected more than the limit of the toner collection capacity of the waste toner box, resulting in the trouble of the overflow of waste toner from the waste toner box and so contamination of the apparatus main body.
To cope with this, a technique to prevent the overflow of waste toner from the waste toner box has been disclosed, for example in JP 2006-154411 A. According to this patent document, as the number of times of the replacement of a waste toner box increases, the number of images that can be formed after the detection of a near-end state decreases.
As stated above, the near-end state of a waste toner box is detected with a detection sensor on the basis of the weight of the waste toner box placed on a waste toner box base. Such a detection of the near-end state based on the weight detection, however, has the problem of a detection error of the near-end state repeating detection and non-detection caused by factors such as vibration of the image forming apparatus main body. Unfortunately, in such a case, a user cannot judge whether or not to replace the waste toner box.
In view of the aforementioned problems, it is an object of the present invention to provide an image forming apparatus capable of preventing a detection error of a near-end state for a waste-toner box.